A dredge of the kind adapted to take samples from the bottom of a body of water is known as a benthic sampling dredge and conventionally comprises a hollow body having closures at its upper and lower ends that are movable between open and closed positions. A conventional benthic dredge has a pair of clamshell jaws adapted to form a closure for the lower end of the body, and such clamshell jaws are pivoted on the body for movements between a position in which the bottom of the body is open to a position in which the clamshell jaws close the bottom of the body. The clamshell jaws conventionally are so constructed that, as they move toward the closed position, they cut a sample from the bottom of the body of water and support the sample whithin the body.
The closure at the upper end of the body is movable from a closed position to an open position, thereby facilitating lowering of the dredge through the body of water, and such closure is adapted to be closed prior to raising the dredge from the bottom, thereby minimizing the possibility of the sample's being washed out of the dredge body.
The clamshell jaws conventionally are spring biased toward their closed position and are releasably latched in their open position. Upon release of the latch, springs move the jaws toward their closed position. A typical dredge of the kind having spring biased clamshell closure jaws is disclosed in U.S. Pat. No. 3,762,078, issued Oct. 2, 1973.
One of the problems associated with conventional, spring biased clamshell jaws is that the driving force of the springs diminishes as the jaws approach their closed position. Consequently, debris which may lie in the path of closing movement of the jaws many times prevents complete closing of the jaws because the springs are incapable of applying sufficient force on the jaws to enable them to sever the obstruction. Thus, a good part of the sample may escape from the dredge as the latter is raised to the surface of the water.
Another disadvantage of spring biased jaws is that, over a period of time, the springs wear and lose some of their strength This, coupled with the reduction in applied force as the jaws move toward their closed position, increases the possibility that the jaws will not close fully and remain closed as the dredge is raised.
Not all benthic dredges in use heretofore have used springs for closing the jaws. Some of the known dredges have utilized a linkage operable to move the clamshell jaws between their open and closed positions. One such dredge is disclosed in Marine Geology, Volume IV, 1966, pages 365-372, and published by Elesiver Publishing Company, Amsterdam. This dredge has a number of disadvantages. For example, the linkage is so arranged that, as the jaws approach their closed position, the closing force is greatly diminished, thereby minimizing the ability of the jaws to cut through an obstruction. Further, the linkage is of such construction that, in some positions of the linkage, portions of the links extend beyond the confines of the dredge, thereby exposing the linkage to the possibility of damage of a kind that could cause malfunction of the jaw closing mechanism. In addition, such damage could adversely affect the mechanism for releasing the jaw closing mechanism and cause the latter to function erratically, particularly in bodies of water where there are currents.
A principal object of the present invention is to provide a benthic dredge which overcomes the above referred to disadvantages of known benthic dredges.